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Abstract

This paper addresses the problem of what is happening physically inside the skull during head-ball contact. Mathematical models based upon Newton’s laws of motion and numerical methods are used to create animations of brain motion and deformation inside the skull.

Initially a 1 cm gap filled with cerebrospinal fluid (CSF) separates the brain from the rigid skull in adults and older children. Whole head acceleration induces a pulse of artificial gravity within the skull. Because brain density differs slightly from that of CSF, the brain accelerates and strikes the inner aspect of the skull, undergoing viscoelastic deformation, ranging from 1 to 2 percent compression for normal heading with good technique, from 5 to 10 percent compression for normal heading with poor technique, and from 30 to 40 percent compression for accidental heading of rising balls at close range. The amount of local strain developed at the point of impact is magnified by force concentration caused by the mismatch between curvature of the brain and curvature of the overlying skull. Computed values are compared to a putative safe level of 1% maximum compressive strain permitted by the skull anatomy of woodpeckers

This fresh biomechanical analysis allows one to visualize events within the skull during soccer heading. The results suggest heading safety is greatly improved when players head the ball with greater effective body mass, which is determined by a player’s size, strength, and technique. Focus on teaching proper technique, re-design of age-appropriate balls with reduced weight, and strict avoidance of head contact with fast, rising balls kicked at close range can substantially reduce the risk of subtle brain injury.